Treatment of Mg powder with carbonic acid and the effect of treatment variables and treated Mg ratios on coating performance in salt spray tests

Magnesium-rich primers (MgRPs) are known to exhibit excellent corrosion resistance during natural weathering due to the formation of a controlled and complex cathodic protective layer which includes but is not limited to changing combinations of magnesium metal, magnesium hydroxide, and magnesium carbonate each during film formation, cure, and environmental exposure. Pretreating Mg powder with carbonic acid before incorporation into coatings has been shown to enhance the corrosion resistance of MgRPs. In an earlier study, the conditions for treating Mg powder and the effects of variables such as time and the order of addition were evaluated to determine optimized treatment conditions. In this study, the treatment process was analyzed further to better understand the nature of the carbonation process and the effect of treatment variables on the overall corrosion protection process. Coatings prepared with different ratios of treated and untreated Mg were evaluated via ASTM B117 salt fog exposure to determine the optimized ratio of treated and untreated pigments for maximum corrosion protection.     

Microstructure and Mechanical Performance of Friction Stir Spot-Welded Aluminum-5754 Sheets

Friction stir spot welding (FSSW) is a recent trend of joining light-weight sheet metals while fabricating automotive and aerospace body components. For the successful application of this solid-state welding process, it is imperative to have a thorough understanding of the weld microstructure, mechanical performance, and failure mechanism. In the present study, FSSW of aluminum-5754 sheet metal was tried using tools with circular and tapered pin considering different tool rotational speeds, plunge depths, and dwell times. The effects of tool design and process parameters on temperature distribution near the sheet-tool interface, weld microstructure, weld strength, and failure modes were studied. It was found that the peak temperature was higher while welding with a tool having circular pin compared to tapered pin, leading to a bigger dynamic recrystallized stir zone (SZ) with a hook tip bending towards the upper sheet and away from the keyhole. Hence, higher lap shear separation load was observed in the welds made from circular pin compared to those made from tapered pin. Due to influence of size and hardness of SZ on crack propagation, three different failure modes of weld nugget were observed through optical cross-sectional micrograph and SEM fractographs.     

Performance evaluation framework for sustainable freight transportation systems

Sustainability in freight transportation demands for a balance among economic, environmental, and social aspects in shipping commodities throughout a supply chain. The performance evaluation of sustainable freight transportation (SFT) systems is of prime importance as it facilitates perpetual and objective assessment for advancements towards sustainability targets. In this study, we propose a comprehensive framework to assess the sustainability performance of freight transportation systems. We pinpoint critical success factors (CSFs) affecting the performance of SFT by carrying out an extensive literature review and conducting a Delphi study to seek experts’ opinions from industry as well as academia. Further, a comprehensive hierarchical framework is developed to establish inter-relationships among these CSFs followed by prioritisation of these CSFs. The application of the proposed framework is illustrated through a case example. This framework would also serve as a reference for decision-makers in selecting the most sustainable freight transportation system.     

Genetic Algorithms for Design of Discrete Phase-only Reconfigurable Array Antennas with Fixed Dynamic Range Ratio

In this paper, we present a new method based on real-coded Genetic Algorithm (GA) with elitist model for optimal design of a reconfigurable symmetrical dual-beam uniformly spaced linear isotropic antenna array with phase-only control of quantized phase shifters. The problem is to find a common amplitude distribution that will generate a pencil beam with zero phases and a flat-top beam with discrete phases of a six-bit discrete phase shifter, without or with pre-fixing the value of dynamic range ratio (|I _max/I _min|) of excitation current amplitude distribution equal to or less than five.     

Characterization of the functional binding properties of antibody conjugated quantum dots

Antibody conjugated quantum dots are an emerging technology for high-resolution labeling of biological systems. In this work we determined the number of functional antibodies (i.e., antibodies that are sterically available for functional binding to target proteins) conjugated to semiconductor quantum dots. This is critical for the interpretation of biological data labeled with these methods. We found that the number of available functional antibodies varied significantly for different conjugation methods and are lower than previously estimated. These results may suggest potential strategies for improving quantum dot labeling of biological preparations.     

Supercritical fluid processing of drug nanoparticles in stable suspension

Significant effort has been directed toward the development of drug formulation and delivery techniques, especially for the drug of no or poor aqueous solubility. Among various strategies to address the solubility issue, the reduction of drug particle sizes to the nanoscale has been identified as a potentially effective and broadly applicable approach. Complementary to traditional methods, supercritical fluid techniques have found unique applications in the production and processing of drug particles. Here we report the application of a newly developed supercritical fluid processing technique, Rapid Expansion of a Supercritical Solution into a Liquid Solvent, to the nanosizing of potent antiparasitic drug Amphotericin B particles. A supercritical carbon dioxide-cosolvent system was used for the solubilization and processing of the drug. The process produced well-dispersed nanoscale Amphotericin B particles suspended in an aqueous solution, and the suspension was intrinsically stable or could be further stabilized in the presence of water-soluble polymers. The properties of the drug nanoparticles were found to be dependent on the type of cosolvent used. The results on the use of dimethyl sulfoxide and methanol as cosolvents and their effects on the properties of nanosized Amphotericin B particles are presented and discussed.     

Electronic stopping dependence of ion beam induced modifications in GaN

We report here Swift heavy ion induced effects in GaN samples grown by metal organic chemical vapor deposition (MOCVD) technique. These samples were irradiated with 80 MeV Ni and 100 MeV Ag ions at a fixed fluence of 1 × 10¹³ ions/cm². Ion species and energies are chosen such that the difference in their electronic energy loss (S_e) would be 8 keV/nm. Effects of Ag on structural and optical properties over Ni ions have been discussed extensively. We employed different characterization techniques like High Resolution X-ray Diffraction (HRXRD) and Raman Spectroscopy for defect density calculations and for vibrational modes, respectively. Defect densities are calculated and compared using Williamson-Hall method from HRXRD. Change of strain and vibrational modes with S_e has been discussed.     

Kinetic investigation of CO2 and N2 clathrate hydrate formation using cyclopentane: Application in desalination

Hydrate-based desalination could be a promising technique for producing fresh water from saline water, as it is an eco-friendly process and suitable for large-scale implementation. To make the hydrate-based desalination technology easily scalable, we looked at using air (or N₂) or CO₂ as a hydrate former, along with cyclopentane (CP). Hydrate former CP helps to reduce the operating conditions, as CP forms hydrate at ambient pressure. However, hydrate formation kinetics due to water-insoluble CP is slow. In this work, the kinetics of hydrate formation in saline water were investigated and compared to identify the utility of CO₂ and N₂ as hydrate formers for desalination work. The addition of CP as a hydrate former should transform the structure of CO₂ hydrate from structure I (sI) to structure II (sII), as CP occupies the large cages (5¹²6⁴) in the gas hydrate. A set of three similar reactors were used for this study to collect data quickly. Furthermore, the triple reactor setup is a unique reactor design mounted on a shaker, and a set of SS-316 balls present inside the horizontal reactor imparts the mixing. Experiments with the CO₂-CP mixture and N₂-CP mixture have been studied in the presence or absence of 3 wt.% NaCl at 274 K and 3 MPa pressure. The gas uptake kinetics, water recovery, and separation efficiency have been investigated.     

Temperature and field induced strain in polycrystalline Ni50Mn35In15−xSix magnetic shape memory Heusler alloys

Magnetic shape memory properties of polycrystalline Ni₅₀Mn₃₅In_15−xSi_x were investigated. A reversible strain of more than 0.4% was observed for x = 0 at a magnetic field H = 5 T that was found to be associated with a field induced reverse martensitic transformation. The strains were found to increase with the substitution of In by Si and strains larger than 1% were observed for x = 2 at H = 5 T. Both the positive and negative strain changes were observed in the vicinity of martensitic transition temperatures. The strain in Ni₅₀Mn₃₅In_15−xSi_x was found to depend on silicon concentration, and on samples texture.     

Epitaxial growth of topological insulator Bi2Se3 film on Si(111) with atomically sharp interface

Atomically sharp epitaxial growth of Bi₂Se₃ films is achieved on Si(111) substrate with molecular beam epitaxy. Two-step growth process is found to be a key to achieve interfacial-layer-free epitaxial Bi₂Se₃ films on Si substrates. With a single-step high temperature growth, second phase clusters are formed at an early stage. On the other hand, with low temperature growth, the film tends to be disordered even in the absence of a second phase. With a low temperature initial growth followed by a high temperature growth, second-phase-free atomically sharp interface is obtained between Bi₂Se₃ and Si substrate, as verified by reflection high energy electron diffraction (RHEED), transmission electron microscopy (TEM) and X-ray diffraction. The lattice constant of Bi₂Se₃ is observed to relax to its bulk value during the first quintuple layer according to RHEED analysis, implying the absence of strain from the substrate. TEM shows a fully epitaxial structure of Bi₂Se₃ film down to the first quintuple layer without any second phase or an amorphous layer.